Storage system for nuclear fuel

ABSTRACT

A fuel storage system for storing and drying nuclear fuel rods includes a vertically oriented capsule defining an internal cavity. A plurality of fuel rod storage tubes is disposed in the cavity. In one embodiment, each storage tube has a transverse cross section configured and dimensioned to hold no more than one fuel rod. Intact or damaged fuel rods may be stored in the storage tubes. After the fuel rods are loaded into the capsule, a lid is attached to a previously open top end of the capsule. In one embodiment, the lid may be sealed welded to the capsule for forming a gas tight enclosure. The interior of the capsule and multiple fuel rods contained therein may be dried together simultaneously via flow conduits formed in the lid that can be fluidly connected to a suitable drying process such as a forced gas dehydration system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/983,606 filed Apr. 24, 2014, which is incorporated herein byreference in its entirety.

BACKGROUND

The present invention relates generally to nuclear fuel containment, andmore particularly to a capsule and related method for storing ortransporting individual nuclear fuel pins or rods including damagedrods.

Reactor pools store used fuel assemblies after removal and dischargefrom the reactor. The fuel assemblies and individual fuel rods thereinmay become damaged and compromised during the reactor operations,resulting in cladding defects, breaking, warping, or other damage. Theresulting damaged fuel assemblies and rods are placed into the reactorpools upon removal and discharge from the reactor core. Eventually, thedamaged fuel assemblies, rods, and/or fuel debris must be removed fromthe pools, thereby allowing decommissioning of the plants.

The storage and transport regulations in many countries do not allowstorage or transport of damaged fuel assemblies without encapsulation ina secondary capsule that provides confinement. Due to the high doserates of used fuel assemblies post discharge, encapsulating fuelassemblies is traditionally done underwater. Furthermore, some countriesmay require removal of individual damaged fuel rods from the fuelassembly and separate storage in such secondary capsules. Processesalready exist for removing single rods from a used fuel assembly andencapsulation. Subsequent drying of damaged fuel after removal from thereactor pool using traditional vacuum drying is exceedingly challengingbecause water can penetrate through cladding defects and become trappedinside the cladding materials.

An improved fuel storage system and method for drying, storing, andtransporting damaged fuel rods is desired.

BRIEF SUMMARY

A nuclear fuel storage system and related method are provided thatfacilitates drying and storage of individual fuel rods, which may beused for damaged and intact fuel rods and debris. The system includes acapsule that is configured for holding a plurality of fuel rods, andfurther for drying the internal cavity of the capsule and fuel rodsstored therein using known inert forced gas dehydration (FGD) techniquesor other methods prior to long term storage. Existing forced gasdehydration systems and methods that may be used with the presentinvention can be found in commonly owned U.S. Pat. Nos. 7,096,600,7,210,247, 8,067,659, 8,266,823, and 7,707,741, which are allincorporated herein by reference in their entireties.

In one embodiment, a storage capsule for nuclear fuel rods includes: anelongated body defining a vertical centerline axis, the body comprisingan open top end, a bottom end, and sidewalls extending between the topand bottom ends; an internal cavity formed within the body; a lidattached to and closing the top end of the body; and an array of axiallyextending fuel rod storage tubes disposed in the cavity; wherein eachstorage tube has a transverse cross section configured and dimensionedto hold no more than one fuel rod.

In one embodiment, a fuel storage system for storing nuclear fuel rodsincludes: an elongated capsule defining a vertical centerline axis, thecapsule comprising a top end, a bottom end, and sidewalls extendingbetween the top and bottom ends; an internal cavity formed within thecapsule; a lid attached to the top end of the capsule, the lid includingan exposed top surface and a bottom surface; an upper tubesheet and alower tubesheet disposed in the cavity; a plurality of verticallyoriented fuel rod storage tubes extending between the upper and lowertubesheets; and a central drain tube extending between the upper andlower tubesheets; wherein each storage tube has a transverse crosssection configured and dimensioned to hold no more than one fuel rod.

A method for storing nuclear fuel rods is provided. The method includes:providing an elongated vertically oriented capsule including an open topend, a bottom end, and an internal cavity, the capsule further includinga plurality of vertically oriented fuel rod storage tubes each having atop end spaced below the top end of the capsule, the storage tubes eachhaving a transverse cross section configured and dimensioned to hold nomore than a single fuel rod; inserting a first fuel rod into a firststorage tube; inserting a second fuel rod into a second storage tube;attaching a lid to the top end of the capsule; and sealing the lid tothe capsule to form a gas tight seal.

A method for storing and drying nuclear fuel rods includes: providing anelongated vertically oriented capsule including an open top end, abottom end, and an internal cavity, the capsule further including aplurality of vertically oriented fuel rod storage tubes each having atop end spaced below the top end of the capsule, the storage tubes eachhaving a transverse cross section configured and dimensioned to hold nomore than a single fuel rod; inserting a fuel rod into each of thestorage tubes; attaching a lid to the top end of the capsule, the lidincluding a gas supply flow conduit extending between top and bottomsurfaces of the lid and a gas return flow conduit extending between thetop and bottom surfaces of the lid; sealing the lid to the capsule toform a gas tight seal; pumping an inert drying gas from a source throughthe gas supply conduit into the cavity of the capsule; flowing the gasthrough each of the storage tubes; collecting the gas leaving thestorage tubes; and flowing the gas through the gas return conduit backto the source.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein likeelements are labeled similarly and in which:

FIG. 1 is a perspective view of a fuel rod storage system comprising acapsule and sealable closure lid;

FIG. 2 is an enlarged view thereof showing the top end of the capsuleand lid installed;

FIG. 3 is an enlarged view thereof showing the top end of the capsuleand lid removed;

FIG. 4 is a top perspective view of the lid;

FIG. 5 is a perspective view thereof showing internal flow conduitsformed in the lid;

FIG. 6 is a bottom perspective view of the lid;

FIG. 7 is a top perspective view showing the inside of the capsule withlid removed, fuel rod storage tubes, and a central drain tube withsealing assembly;

FIG. 8 is a cross-sectional perspective view of the capsule showing theinternals;

FIG. 9A is a side elevation cross-sectional view thereof;

FIG. 9B is an enlarged detail taken from FIG. 9A;

FIG. 10A is a detailed view of a top corner of the capsule showing thelid in place but not sealed and coupled to the capsule;

FIG. 10B is a view thereof showing the formation of a seal weld tocouple to the lid to the capsule;

FIG. 11 is top perspective view of a lid of a transport cask with twofuel rod storage capsules mounted therein;

FIG. 12 is an enlarged perspective view of one of the capsules of FIG.11;

FIG. 13 is a cross-sectional perspective view of the transport cask ofFIG. 11 showing the capsules;

FIG. 14 is an enlarged view from FIG. 11 showing a pair of remoteoperated valve assemblies installed in the lid of the capsule for gasdrying the interior of the capsule;

FIG. 15 is cross-sectional perspective view showing of FIGS. 11 and 14showing one of the capsules mounted in the lid of the transport cask;

FIG. 15A is an enlarged view from FIG. 15 showing the mounting and welddetail coupling the lid to the top end of the capsule;

FIG. 16 is a perspective view of a leak testing lid attachable to thecapsule;

FIG. 17 is a perspective view of the capsule and a lifting assembly; and

FIG. 18 is an enlarged view thereof of the lid and lifting assemblyconnection.

All drawings are schematic and not necessarily to scale.

DETAILED DESCRIPTION

The features and benefits of the invention are illustrated and describedherein by reference to exemplary embodiments. This description ofexemplary embodiments is intended to be read in connection with theaccompanying drawings, which are to be considered part of the entirewritten description. Accordingly, the disclosure expressly should not belimited to such exemplary embodiments illustrating some possiblenon-limiting combination of features that may exist alone or in othercombinations of features.

In the description of embodiments disclosed herein, any reference todirection or orientation is merely intended for convenience ofdescription and is not intended in any way to limit the scope of thepresent invention. Relative terms such as “lower,” “upper,”“horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and“bottom” as well as derivative thereof (e.g., “horizontally,”“downwardly,” “upwardly,” etc.) should be construed to refer to theorientation as then described or as shown in the drawing underdiscussion. These relative terms are for convenience of description onlyand do not require that the apparatus be constructed or operated in aparticular orientation. Terms such as “attached,” “affixed,”“connected,” “coupled,” “interconnected,” and similar refer to arelationship wherein structures are secured or attached to one anothereither directly or indirectly through intervening structures, as well asboth movable or rigid attachments or relationships, unless expresslydescribed otherwise.

As used throughout, any ranges disclosed herein are used as shorthandfor describing each and every value that is within the range. Any valuewithin the range can be selected as the terminus of the range. Inaddition, all references cited herein are hereby incorporated byreferenced in their entireties. In the event of a conflict in adefinition in the present disclosure and that of a cited reference, thepresent disclosure controls.

nuclear fuel assemblies (also referred to as “bundles” in the art) eachcomprise a plurality of fuel pins or rods mechanically coupled togetherin an array which is insertable as a unit into a reactor core. The fuelassemblies traditionally have a rectilinear cross-sectionalconfiguration such as square array and contain multiple fuel rods. Areactor core contains multiple such fuel assemblies.

The fuel rods are generally cylindrical elongated metal tubularstructures formed of materials such as zirconium alloy. The tubes hold aplurality of vertically-stacked cylindrical fuel pellets formed ofsintered uranium dioxide. The fuel rod tubes have an external metalcladding formed of corrosion resistant material to prevent degradationof the tube and contamination of the reactor coolant water. The oppositeends of the fuel rod are sealed.

FIGS. 1-9B show a damaged nuclear fuel storage system 100 according tothe present disclosure. The system includes a vertically elongated fuelrod enclosure capsule 110 configured to hold multiple damaged fuel rodsand a closure lid 200 mounted thereto. The lid 200 is configured forcoupling and permanent sealing to the capsule 200, as further describedherein.

Capsule 110 has an elongated and substantially hollow body formed by aplurality of adjoining sidewalls 118 defining an internal cavity 112that extends from a top end 114 to a bottom end 116 along a verticalcenterline axis Cv. The bottom end 116 of the capsule is closed by awall. The top end 114 of the capsule is open to allow insertion of thedamaged rods therein. The sidewalls 118 are sold in structure so thatthe cavity 112 is only accessible through the open top end 114 beforethe lid is secured on the capsule.

In one embodiment, capsule 110 may have a rectilinear transversecross-sectional shape such as square which conforms to the shape of atypical fuel assembly. This allows storage of the capsule 110 in thesame type of radiation-shielded canister or cask used to store multiplespent fuel assemblies, for example without limitation a multi-purposecanister (MPC) or HI-STAR cask such as those available from HoltecInternational of Marlton, N.J. Such canisters or casks have an internalbasket with an array of rectilinear-shaped openings for holdingsquare-shaped fuel assemblies. It will be appreciated however that othershaped capsules 110 may be used in other embodiments and applications.

The body of the capsule 110 may be formed of any suitable preferablycorrosion resistant material for longevity and maintenance of structuralintegrity. In one non-limiting exemplary embodiment, the capsule 110 maybe made of stainless steel and have a nominal wall thickness of 6 mm.

In certain embodiments, the capsule 110 may further include a laterallyenlarged mounting flange 111 disposed at and adjacent to the top end114, as shown in FIGS. 1-3 and 7-9A. Mounting flange 111 extendslaterally outwards from the sidewalls 118 on all sides and verticallydownwards from top end 114 along the sidewalls for a short distance. Themounting flange 111 is configured and dimensioned to engage a mountingopening 302 formed in a storage canister 300, thereby supporting theentire weight of a loaded capsule 110 in a vertically cantileveredmanner as shown in FIGS. 11-13 and further describe herein. In otherembodiments, different methods may be used to support the capsule 110 inthe storage canister and mounting flange 111 may be omitted.

Referring now particularly to FIGS. 3, 7, 8 and 9A, the capsule 110further includes an internal basket assembly configured to store andsupport a plurality of damaged fuel rods. The assembly includes an uppertubesheet 120 and lower tubesheet 122 spaced vertically apart therefrom.The upper and lower tubesheets are horizontally oriented. The lowertubesheet 122 is separated from the interior bottom surface 116 a ofbottom end 116 of the capsule 110 by a vertical gap to form a bottomflow plenum 124. The upper tubesheet 120 is spaced vertically downwardsfrom the top end 112 of the capsule 110 by a distance D1 sufficient toform a top flow plenum 126 when the closure lid 200 is mounted on thecapsule as shown in FIG. 15. Top plenum 126 is therefore formed betweenthe bottom 204 of the lid 200 and top surface 128 of the upper tubesheet120. Both the bottom and top plenums 124, 126 are part of flow pathsused in conjunction with the gas fuel rod drying/dehydration processafter the capsule is closed and sealed, as further described herein.

A plurality of fuel rod storage tubes 130 are each supported by theupper and lower tubesheets 120, 122 for holding the damaged (i.e. brokenand/or leaking) fuel rods. In certain embodiments, intermediatesupporting tubesheets or other support elements (not shown) may be usedto provide supplementary support and lateral stability to the storagetubes 130 for seismic events. In one embodiment, the storage tubes 130each have a diameter and internal cavity 131 with a transverse crosssection configured and dimensioned to hold no more than a single fuelrod. Accordingly, the tubes 130 extend vertically along and parallel tothe vertical centerline axis Cv of the capsule 110 from the uppertubesheet 120 to the lower tubesheet 122. Each of the tubes 130 isaccessible through the upper tubesheet 120 (see, e.g. FIG. 9A). In oneembodiment, the tubes 130 each have an associated machined lead-in guidein the upper tubesheet 120 to support the insertion of the fuel rods. Anannular tapered or chamfered entrance 136 is therefore formed in theupper tubesheet 120 adjacent and proximate to the top open end 132 ofeach tube 130. The obliquely angled surface (with respect to thevertical centerline axis Cv) of the chamfered entranceways 136 helpcenter and guide loading of the damaged fuel rods into each of thestorage tubes 130. The top end 132 of the tubes may therefore be spacedslightly below the top surface 128 of the upper tubesheet 120 as shown.

The bottom ends 134 of the fuel rod storage tubes 130 may rest on thebottom interior surface 116 a of the capsule 110. Each storage tube 130includes one or more flow openings 133 of any suitable shape locatedproximate to the bottom ends 134 of the tubes below the bottom tubesheet122. The openings 133 allow gas to enter the tubes from the bottomplenum 124 during the forced gas dehydration process and rise upwardthrough the tubes to dry the damaged fuel rods.

The fuel rod storage tubes 130 may be mounted in the upper and lowertubesheets 120, 122 by any suitable method. In certain embodiments, thetubes 130 may be rigidly coupled to upper and/or lower tubesheets 120,122 such as by welding, soldering, explosive tube expansion techniques,etc. In other embodiments, the tubes 130 may be movably coupled to theupper and/or lower tubesheets to allow for thermal expansion when heatedby waste heat generated from the decaying fuel rods and heated forcedgas dehydration. Accordingly, a number of possible rigid and non-rigidtube mounting scenarios as possible and the invention is not limited byany particular one.

The fuel rod storage tubes 130 may be arranged in any suitable patternso long as the fuel rods may be readily inserted into each tube withinthe fuel pool. In the non-limiting exemplary embodiment shown, the tubes130 are circumferentially spaced apart and arranged in a circular arrayaround a central drain tube 150 further described below. Otherarrangements and patterns may be used.

Referring now to FIGS. 7, 8, 9A, 9B, and 15, the central drain tube 150of the capsule 110 may be mounted at approximately the geometric centerof the upper tubesheet 120 as shown. The center drain tube 150 in onearrangement is supported by and extends vertically parallel to andcoaxially with centerline axis Cv of the capsule from the uppertubesheet 120 to the bottom tubesheet 122. The drain tube 150 may berigidly coupled to the tubesheets 120, 122 using the same techniquesdescribed herein for the fuel rod storage tubes. Drain tube 150 is ahollow structure forming a pathway for introducing insert drying gasinto the tube assembly to dry the interior of capsule 110 followingclosure and sealing, as further described herein.

The drain tube 150 includes an open top end 151 and an open bottom end152. The top end functions as a gas inlet and the bottom end functionsas a gas outlet, with respect to the dehydration gas flow path furtherdescribed herein. The bottom end 152 is open into and may extendslightly below the bottom surface of the lower tubesheet 122 to placethe drain tube in fluid communication with the bottom plenum 124 of thecapsule 110, as shown for example in FIGS. 9A-B. This forms a fluidpathway for introducing drying gas into the bottom of the capsule 110.The outlet end 152 of the drain tube 150 is spaced vertically apart fromthe interior bottom surface 116 a of the capsule 110.

Drain tube 150 may include a sealing feature configured to form asubstantially gas-tight seal between the closure lid 200 and drain tubefor forced gas dehydration process. In one embodiment, the sealingfeature may be a spring-biased sealing assembly 140 configured to engageand form a seal with the bottom of the closure lid 200 for gas drying.The sealing assembly 140 includes a short inlet tube 141, an enlargedresilient sealing member 142 disposed on top of the inlet tube, andspring 143. Inlet tube 141 has a length less than the length of thedrain tube 150. Spring 143 may be a helical compression spring in oneembodiment having a top end engaging the underside 142 b of the sealingmember 142 which extends laterally (i.e. transverse to verticalcenterline axis Cv) and diametrically beyond the inlet tube 141, and abottom end engaging the top surface 128 of the upper tubesheet 120. Theinlet tube 141 is rigidly coupled to the sealing member 142 and has adiameter slightly smaller than the drain tube 150. This allows the lowerportion of the inlet tube 141 to be inserted into the upper portion ofthe drain tube 150 through the top inlet end 151 for upward/downwardmovement in relation to the drain tube. Spring 143 operates to bias thesealing member 142 and inlet tube 141 assembly into an upward projectedinactive position away from the upper tubesheet 120 ready to engage theclosure lid 200, as further described herein. Accordingly, the sealingassembly 140 is axially movable along the vertical centerline axis fromthe upward projected inactive position to a downward active sealingposition.

In one embodiment, the sealing member 142 may have a circular shape intop plan view and a convexly curved or domed sealing surface 142 a inside transverse cross-sectional view (see, e.g. FIGS. 9A and 9B). Thecurved sealing surface 142 a ensures positive sealing engagement with agas supply outlet extension tube 210 in the capsule closure lid 200 (seeFIG. 6) to compensate for irregularities in the extension tube endsurface edges and less than exact centering of the extension tube withrespect to the sealing member 142, thereby preventing substantialleakage of drying gas when coupled together. The sealing member 142includes a vertically oriented through-hole 144 to form a fluid pathwaythrough the sealing member to the drain tube 150.

In one embodiment, the sealing member 142 may be made of a resilientlydeformable elastomeric material suitable for the environment of aradioactive damaged fuel rod storage capsule. The elastomeric sealprovides sufficient sealing and a leak-resistant interface between thecentral drain tube 150 and closure lid 200 to allow the inert drying gas(e.g. helium, nitrogen, etc.) to be pumped down the central drain tubeto the bottom of the capsule 110 during the forced gas dehydrationprocess.

It will be appreciated that other types of seals and arrangements may beused. Accordingly, in some embodiments metal or compositemetal-elastomeric sealing members may be used. The sealing member mayalso have other configurations or shapes instead of convexly domed, suchas a disk shaped with a flat top surface or other shape. In otherembodiments, a non-spring activated sealing assembly may be used.Accordingly, the invention is not limited by the material ofconstruction or design of the seal and sealing assembly so long as arelatively gas-tight seal may be formed between the closure lid gasoutlet extension tube 210 and the drain tube 150 for forced gasdehydration of the capsule 110.

The fuel rod basket assembly, including the foregoing tubesheets, rodstorage tubes, central drain tube, and sealing assembly may be made ofany suitable preferably corrosion resistant material such as stainlesssteel. Other appropriate materials may be used.

The closure lid 200 will now be further described.

Referring to FIGS. 1-6 and 15, lid 200 in one embodiment may have agenerally rectilinear cube-shaped body to complement the shape of cavity112 in capsule 110 in which at least a portion of the lid is received.Accordingly, in one embodiment the lid 200 and capsule 110 may have asquare shape in top plan view. Lid 200 further has a substantially solidinternal structure except for the gas flow conduits formed therein, asfurther described below. The lid 200 is formed of a preferably corrosionresistant metal, such as stainless steel. Other materials may be used.

Lid 200 includes a top surface 202, bottom surface 204, and lateralsides 206 extending between the top and bottom surfaces. The lateralsides 206 of the lid have a width sized to permit insertion of amajority of the height of the lid into the cavity 112 of the capsule.The bottom of the lid 200 includes a peripheral skirt 212 extendingaround the perimeter of the bottom surface 204 that engages and rests onthe top surface 128 of the upper tubesheet 120 of the capsule 110 whenthe lid is mounted in the capsule. In one embodiment, the skirt 212 iscontinuous in structure and extends around the entire perimeter withoutinterruption. The skirt 212 projects downward for a distance from thebottom surface 204 of the lid which is recessed above the bottom edge212 a of the skirt. The forms a downwardly open space 211 having a depthcommensurate with the height of the skirt 212. When the bottom edge 212a of skirt 212 rests on top surface 128 of the upper tubesheet 120, thetop plenum 126 is formed between the bottom surface 204 of lid 200 andthe upper tubesheet inside and within the skirt 212. The bottom edge 212a of the skirt 212 thereby forms a seal between the upper tubesheet 120and lid 200 for forced gas dehydration of the capsule 110.

An enlarged seating flange 208 extends around the entire perimeter ofthe lid 200 adjacent to top surface 202 and projects laterally beyondthe sides 206. The top surface 202 may be recessed below the top edge208 a of the seating flange 208 as shown. A stepped shoulder 213 isformed between seating flange 208 and sides 206 which engages and seatson a mating shoulder 113 formed inside the mounting flange 111 ofcapsule 110 in cavity 112 (see particularly FIG. 15A). Both matingshoulders 213 and 113 extend around the entire perimeter regions of thelid 200 and capsule 110 respectively and limit the insertion depth ofthe lid into the capsule.

In one embodiment, the top edges 111 a and 208 a of the mounting flange111 and seating flange 208 respectively are flush with each other andlie in approximately the same horizontal plane when the closure lid 200is fully mounted in the capsule 110 (see, e.g. FIGS. 10A, 10B, and 15A).This facilitates formation of an open V-groove weld 205 to hermeticallyseal the lid to the capsule. The mounting and seating flanges 111, 208each include opposing beveled faces 115, 208 respectively to form theV-groove. Because of the recessed top surface 202 of the lid 200 andmounting flange 111, access is available to both sides of finished weldwhich advantageously permits full volumetric inspection of the weld suchas by ultrasonic non-destructive testing or other methods. The sourceand detector of the ultrasonic test (UT) equipment may therefore beplaced on opposite sides of the weld for full examination. A multi-passwelding process may be used which prevents any potentialthrough-cracking of a single weld line in the case of an undetecteddefect. This parallels welding processes used in the United States forMulti-Purpose Canisters (MPCs), but is modified to allow volumetric weldexamination (a key consideration for acceptance of weld integrity bysome international regulators). Each pass is followed by a LiquidPenetrant Test (LPT) to identify defects in the weld layer as the weldis formed. The finished weld is then volumetrically tested using UT.Unlike a bolted joint sealed with gaskets, a welded joint withvolumetric inspection typically does not require leak-monitoring orchecks prior to future transport. FIGS. 10A and 10B show the lid 200 andcapsule 110 before and after welding, respectively. This does not limitthe capsule to having a bolted lid, similar to dual-purpose metal casksused for storage and transport of spent nuclear fuel. In suchembodiment, the capsule would have one more seals, for exampleelastomeric or metallic, that would be compressed during tightening ofthe lid bolts on the capsule, forming a hermetic seal.

According to another aspect of the invention, the closure lid 200 isconfigured to permit forced gas dehydration of the capsule 110 andplurality of damaged fuel rods contained therein after the lid is sealwelded to the capsule. Accordingly, the lid 200 includes a combinationof gas ports and internal fluid conduits to form a closed flow loopthrough capsule 110. Referring now to FIGS. 1-6 and 15, lid 200 includesa gas supply port 220 and gas return port 222 formed in the top surface202 of the lid, and a gas supply outlet 224 and gas return inlet 226formed in the bottom surface 204 of the lid. In one configuration, thegas supply outlet 224 and return inlet 226 may be located at diagonallyopposite corner regions of the top surface 202 of the lid 200 proximateto the lateral sides 206. The gas supply port 220 is fluidly coupled tothe gas supply outlet 224 via an internal flow conduit 228. The gasreturn port 222 is fluidly coupled to the gas return inlet 226 viaanother separate internal flow conduit 230 which is fluidly isolatedfrom flow conduit 228.

In one embodiment, the flow conduits 228, 230 each follow a torturousmulti-directional path through the lid to prevent neutron streaming. Inone configuration, flow conduit 228 includes a vertical section 222 aconnected to gas supply outlet 224, first horizontal section 228 bconnected thereto, second horizontal section 228 c connected thereto,and second vertical section 228 d connected thereto and gas supply port220. The flow conduit sections 228 a-d may be arranged in a rectilinearpattern. Flow conduit 228 includes a vertical section 230 a connected togas return port 222, horizontal section 230 b connected thereto, andsecond vertical section 230 c connected thereto and gas return inlet226. The flow conduit sections 230a-c may also be arranged in arectilinear pattern. Because the lid 200 has a solid internal structure,the flow conduits may be formed by drilling or boring holes through thelateral sides 206 and top and bottom surfaces 202, 204 of the lid topoints of intersection between the conduits as best shown in FIGS. 5 and15. After formation of the flow conduits, the penetrations 232 in thelateral sides 206 of the lid may be closed using threaded and/or sealwelded metal caps applied before mounting and welding the lid 200 to thecapsule 110. The penetrations 232 in the bottom surface 204 of the lidmay remain open. The gas supply and return port penetrations 232 in thetop surface 202 of the lid may be threaded and closed using threadedcaps 234 to permit removal and installation of remote valve operatingassemblies 240 (RVOAs) for forced gas dehydration of the capsule, asshown in FIGS. 14 and 15.

It should be noted that the gas supply outlet 224 in lid 200 is fluidlycoupled to the gas supply outlet extension tube 210. The extension tube210 compensates for the height of the lid bottom skirt 212 to allowphysical coupling of the tube to the sealing assembly 140 when the skirtrests on the top surface 128 of the upper tubesheet 120. In oneembodiment, the extension tube 210 and gas supply outlet 224 arecentered on the bottom surface 204 of the lid 200. In certain otherembodiments, the extension tube may be omitted and the gas supply outlet224 penetration may be directly coupled to the sealing assembly 140.

A method for storing and drying fuel rods using capsule 110 will now bebriefly described. The method may be used for storing intact or damagedfuel rods, either of which may be stored in capsule 110.

The process begins with the top of the capsule 110 being open so thatthe storage tubes 130 are accessible for loading. The loading operationinvolves inserting the fuel rods into the storage tubes 130. After thecapsule is fully loaded, the lid 200 is attached to the top end 114 andsealed to the capsule. In one preferred embodiment, the lid is sealedwelded to the capsule as described elsewhere herein to form a gas tightseal

After lid 200 is seal welded to the capsule 110, the interior of thecapsule and fuel rods therein may be dried using heated forced gasdehydration (FGD) system such as those available from HoltecInternational of Marlton, N.J. Commonly owned U.S. Pat. Nos. 7,096,600,7,210,247, 8,067,659, 8,266,823, and 7,707,741, which are allincorporated herein by reference in their entireties, describe suchsystems and processes as noted above.

The remote operated valve assemblies 240 are first installed in the gassupply and gas return ports 220, 222. The valves are then connected tothe gas supply and return lines from the FGD system. The next steps,described in further detail herein, include pumping the inert drying gasfrom the FGD system or source through the gas supply conduit into thecavity 112 of the capsule 110 and into the bottom plenum 124, flowingthe gas through each of the storage tubes 130 to dry the fuel rods,collecting the gas leaving the storage tubes in the top plenum 126, andflowing the gas through the gas return conduit back to the FGD source.The process continues for a period of time until analysis of the dryinggas shows an acceptable level of moisture removal from the capsule 110.

Referring now to FIGS. 5, 9A, 14, and 15, threaded caps 234 may first beremoved from the gas supply and return ports 220 and 222 in the lid 200which is welded to the capsule 110. A remote valve operating assembly240 is then threadably coupled to each port 220, 222. The gas supply andreturn lines from the FGD skid which holds the dehydration systemequipment are then fluidly coupled to the valve assemblies. Thedehydration and drying process is now ready to commence by pumping theinert and heat drying gas from the FGD system through the capsule 110 todry the fuel rods in the storage tubes 130, as further described herein.

Gas supplied from the FGD system first flows through the first valveassembly 240 into the lid 200 through the gas supply port 220. Thesupply gas then flows through flow conduit 228 to the gas supply outlet224 and then into gas supply outlet extension tube 210. The supply gasenters the sealing assembly 140 and flows downwards through the centraldrain tube 150 into the bottom plenum 124 of the capsule 110. The gas inthe bottom plenum enters the bottom of the fuel rod storage tubes 120through openings 133 formed in and proximate to the bottom ends 134 ofthe tubes. The gas flows and rises upwards through each of the storagetubes 120 to dry the damaged fuel rods stored therein. The gas thenenters the top plenum 126 above the upper tubesheet 120 beneath the lid200. From here, the gas leaves the top plenum and enters the gas returninlet 226 in the lid. The gas flows through flow conduit 230 to the gasreturn port 222 and into the remote valve operating assembly 240connected thereto. The return gas then flows through the return lineback to the FGD system skid to complete the closed flow loop.

Advantageously, the present invention allows drying of multiple damagedfuel rods in the capsule 110 simultaneously instead of on an individual,piece-meal basis. This saves time, money, and operator dosage ofradiation.

According to another aspect of the invention, the lid 200 includes athreaded lifting port 340 configured for temporary coupling to a liftingassembly 342 that may be used for moving and transporting the capsule110 around the fuel pool and loading into transport casks ormulti-purpose canisters. The lifting assembly 342 in one embodiment mayinclude a lifting rod 344 including a bottom threaded end 346 forrotatable coupling to the threaded lifting port 340 and an opposite topoperating end 348 configured for rigging to equipment such as a cranethat may be used to lift and maneuver the capsule 110.

According to yet another aspect of the invention, a lid-based capsulestorage system is provided which is configured for holding andsupporting a plurality of capsules 110. The capsule storage systemincludes a cask loading lid 400 which may be configured to retrofit andreplace lids used in existing transport or transfer casks used forloading, storing, and transporting undamaged fuel bundles. Using thetemporary lid, the existing casks may used to provide radiationshielding during the capsule 110 drying and closure operations describedherein.

Referring to FIGS. 11-15, the loading lid 400 can be designed for anydual-purpose metal casks, such as those supplied by Holtec, TNI, or GNSor transfer casks, such as the HI-STRAC used by Holtec International inMarlton, N.J. Loading lid 400 may have multiple mounting cutouts oropenings 302 extending completely through the lid each of which aredesigned to allow insertion of a single capsule 110. The mountingopenings 302 are sized smaller than the mounting flange 111 of thecapsule 110 so that the flange remains above the top surface 402 of thelid 400. A shoulder 404 is formed beneath each mounting flange 111between the flange and sidewalls 118 of the capsule which engages thetop surface 402 of the lid 400. This allows the capsules to hang fromthe lid 400 in a vertically cantilevered manner. The top of the capsule110 therefore sites about 10-15 mm above the lid surface 402 in onerepresentative non-limiting embodiment to enable workers to easilyaccess the top of the capsules to perform the closure operations. Thelocation of the mounting openings 302 can be optimized to allow easyworker access to the capsules during the drying and closure operations.

According to another aspect of the invention shown in FIG. 16, a leaktesting lid 500 is provided which can be coupled and sealed to themounting flange 111 of the capsule 110. The lid 500 attached to themounting flange 111 of capsule 110 and includes a piping connectionassembly 502 which allows hook-up to leak testing equipment forperformance of an integrated leak test of the entire sealed capsule 110.

Although the fuel rod encapsulation capsule is described herein for usewith damaged fuel rods, it will be appreciated that the capsule hasfurther applicability for use with intact fuel rods or debris storage aswell. Accordingly, the invention is expressly not limited for use withdamaged fuel rods alone.

While the foregoing description and drawings represent some examplesystems, it will be understood that various additions, modifications andsubstitutions may be made therein without departing from the spirit andscope and range of equivalents of the accompanying claims. Inparticular, it will be clear to those skilled in the art that thepresent invention may be embodied in other forms, structures,arrangements, proportions, sizes, and with other elements, materials,and components, without departing from the spirit or essentialcharacteristics thereof. In addition, numerous variations in themethods/processes described herein may be made. One skilled in the artwill further appreciate that the invention may be used with manymodifications of structure, arrangement, proportions, sizes, materials,and components and otherwise, used in the practice of the invention,which are particularly adapted to specific environments and operativerequirements without departing from the principles of the presentinvention. The presently disclosed embodiments are therefore to beconsidered in all respects as illustrative and not restrictive, thescope of the invention being defined by the appended claims andequivalents thereof, and not limited to the foregoing description orembodiments. Rather, the appended claims should be construed broadly, toinclude other variants and embodiments of the invention, which may bemade by those skilled in the art without departing from the scope andrange of equivalents of the invention.

1. A storage capsule for nuclear fuel rods, the capsule comprising: anelongated body defining a vertical centerline axis, the body comprisingan open top end, a bottom end, and sidewalls extending between the topand bottom ends; an internal cavity formed within the body; a lidattached to and closing the top end of the body; an array of axiallyextending fuel rod storage tubes disposed in the cavity; an uppertubesheet and a lower tubesheet, the upper and lower tubesheetssupporting a top end and a bottom end of each storage tube; a top plenumformed between the lid and upper tubesheet, and a bottom plenum formedbetween the lower tubesheet and the bottom end of the capsule; and acentral drain tube extending parallel to the vertical centerline axisbetween the upper and lower tubesheets, the drain tube in fluidcommunication with the bottom plenum; wherein each storage tube has atransverse cross section configured and dimensioned to hold no more thanone fuel rod. 2.-4. (canceled)
 5. The capsule according to claim 1,wherein the central drain tube is fluidly isolated from the top plenumby a sealing assembly fluidly coupled between a top end of the draintube and the lid.
 6. The capsule according to claim 1, wherein hecentral drain tube is supported by the upper and lower tubesheets. 7.The capsule according to claim 1, wherein the top ends of the storagetubes are in fluid communication with the top plenum and the bottom endsof the storage tubes are in fluid communication with the bottom plenum.8. The capsule according to claim 7, wherein the bottom ends of storagetubes extend below the lower tubesheet into the bottom plenum and reston a bottom interior surface of the capsule.
 9. The capsule according toclaim 8, further comprising at least one flow opening formed near thebottom ends of each storage tube.
 10. The capsule according to claim 1,wherein the lid has a solid structure that defines a first gas supplyflow conduit in fluid communication with the central drain tube andbottom plenum, and a second gas return flow conduit in fluidcommunication with the top plenum and storage tubes. 11.-18. (canceled)19. The capsule according to claim 1, wherein the lid includes athreaded opening for attaching a lifting assembly for moving andtransporting the capsule.
 20. A fuel storage system for storing nuclearfuel rods, the system comprising: an elongated capsule defining avertical centerline axis, the capsule comprising a top end, a bottomend, and sidewalls extending between the top and bottom ends; aninternal cavity formed within the capsule; a lid attached to the top endof the capsule, the lid including an exposed top surface and a bottomsurface; an upper tubesheet and a lower tubesheet disposed in thecavity; a plurality of vertically oriented fuel rod storage tubesextending between the upper and lower tubesheets; a central drain tubeextending between the upper and lower tubesheets; wherein each storagetube has a transverse cross section configured and dimensioned to holdno more than one fuel rod.
 21. The storage system according to claim 20,further comprising a top plenum formed between the lid and uppertubesheet, and a bottom plenum formed between the lower tubesheet andthe bottom end of the capsule.
 22. The storage system according to claim21, wherein the lid includes a first gas supply flow conduit in fluidcommunication with the bottom plenum and a second gas return flowconduit in fluid communication with the top plenum.
 23. The storagesystem according to claim 22, wherein the gas supply flow conduitincludes a gas supply port formed in the top surface of the lid and agas supply outlet formed in the bottom surface of the lid.
 24. Thestorage system according to claim 23, further comprising a sealingassembly fluidly coupling the gas supply outlet in the lid to thecentral drain tube for forming a leak tight connection.
 25. The storagesystem according to claim 24, wherein the sealing assembly included aspring-biased sealing member configured to engage the gas supply outletin the lid.
 26. The storage system according to claim 25, wherein thesealing member is formed of an elastomeric or metallic material.
 27. Thestorage system according to claim 24, further comprising a gas outletextension tube extending downwards from the bottom surface of the lid,the extension tube fluidly coupled to the sealing assembly.
 28. Thestorage system according to claim 27, wherein the central drain tube andgas extensions tube are coaxially aligned with the vertical centerlineaxis of the capsule.
 29. The storage system according to claim 21,further comprising a peripheral skirt extending around a perimeter ofthe bottom surface, the skirt resting on the upper tubesheet to definethe top plenum when the lid is attached to the capsule.
 30. The storagesystem according to claim 22, wherein the lid includes a gas supply portformed in the top surface of the lid in fluid communication with the gassupply flow conduit, and a gas return port formed in the top surface ofthe lid in fluid communication with the gas return flow conduit, the gassupply and return ports each configured for mounting a remote valveoperating assembly thereto for forced gas dehydration of the fuel rods.31. The storage system according to claim 20, wherein lid is fullyinserted the top end of the capsule so that the lid does not protrudesubstantially above the top edge of the capsule 32.-40. (canceled)